Benzyl sulfonium salts



United States Patent 3,409,660 BENZYL SULFONIUM SALTS William G. Lloyd,Dover, N.J., assignor to The Dow Chemical Company, Midland, Mich., acorporation of Delaware No Drawing. Continuation-impart of applicationSer. No. 260,300, Feb. 21, 1963. This application Aug. 15, 1966, Ser.No. 572,178

8 Claims. (Cl. 260-470) ABSTRACT OF THE DISCLOSURE New benzyl sulfoniumsalts have been prepared which are active cationic surfactants, readilyand irreversibly converted into an inert, hydrophobic residue by heatingor drying.

This is a continuation-in-part of application Ser. No. 260,300 filed onFeb. 21, 1963, by William G. Lloyd, now abandoned.

This invention relates to water-soluble cationic surfactants which arereadily and irreversibly converted into inert, hydrophobic residues uponbeing heated or dried. More specifically it concerns new benzylsulfonium salts which combine the hydrophobic properties of certainsubstituent groups with a thermally sensitive methylenesulfonium groupto obtain a cationic surfactant which can be irreversibly converted intoan inert hydrophobic residue by heating or drying.

Organic surfactants are widely used to provide stable aqueous emulsionsfor such commercial products as paper sizing, floor waxes, latex paints,and heavy-duty laundry compositions. The advantages of water-basedsystems are reflected in the ready consumer acceptance of theseproducts.

In many applications it is desirable to form a waterresistant protectivefilm by drying such an emulsion. Yet the water-resistance of such filmsis inherently weakened by the hydrophilic character of the surfactantretained in the film. Also in emulsion polymerization processes, itwould be advantageous at times to replace one surfactant with another ifthe initial surfactant could be removed or destroyed. For example, asurfactant that is desirable during latex polymerization may not besuitable for stabilization of the final product for storage.

It has now been discovered that certain water-soluble benzyl sulfoniumsalts ar active surfactants which can be readily and irreversiblyconverted into non-polar and hydrophobic residues which have negligiblesurfactant properties. These water-soluble sulfonium salts have theformula:

wherein (1) R is a C -C alkyl group and R and R are independently a C -Calkyl or C C hydroxyalkyl group; or (2) R is a C -C alkyl group, R is aC C alkyl group, and R is a group of the formula:

0 (onHm oRr wherein R is a C C alkyl group, and n is an integer from 1to 4; and Y is a counteranion. These fugitive cationic surfactants areeasily prepared in an aqueous solution suitable for use in conventionallatex polymeriza tion processes. These sulfonium salts have in commonthe property of readily and irreversibly degrading upon heating ordrying to form an inert hydrophobic residue. However, by varying thesubstituent groups within the 3,409,660 Patented Nov. 5, 1968 statedrange, salts with varying surfactant characteristics and thermalstabilities can be obtained thus permitting selection of the propertiesmost suitable for a given application.

The term water-soluble as employed herein means dispersible in water toprovide a visually homogeneous and substantially transparent solutioninfinitely dilutable with water.

The novel fugitive cationic surfactants described herein areconveniently prepared by reacting a suitable alkylbenzyl halide with anappropriate organic sulfide according to the equation:

wherein R R and R are as defined above, and X is chlorine or bromine. Ithas been found that when R and R are C -C alkyl or C C hydroxyalkylgroups R, must be at least a C and preferably a C -C alkyl group foractive surfactant properties. But when R;, is an acyloxyalkyl group,e.g. C,,H COOR effective surfactant properties are achieved when R is aC or higher alkyl group.

Many organic sulfides suitable for the synthesis of these sulfoniumsalts are commercially available, such as dimethyl sulfide, diethylsulfide and thiodiglycol. Others can be prepared by known methods. Forexample, several syntheses for 3-alkylthiopropionic esters are given byRapoport et al., J. Am. Chem. Soc., 69, 693 (1947). The addition of analkyl mercaptan to an acrylic or methacrylic ester is particularlysuitable for the purposes of the present invention. For ease ofsynthesis, an organic sulfide with at least one alkyl group containingnot more than two carbons is preferred.

Reaction of the alkylbenzyl halide and organic sulfide is advantageouslycarried out in water or a similar polar hydroxylic solvent such as a C-C alcohol or glycol or aqueous solution thereof. By using an aqueoussolvent and substantially stoichiometric proportions of the reac tants,i.e., about 0.91.1 mole of organic sulfide per mole of benzyl halide,aqueous solutions containing 20-30 wt. percent or more of the sulfoniumsalts can be prepared. Such solutions can be used as a concentrate ofthe surfactant in many applications without isolation or purification ofthe sulfonium salt.

This process for preparing the sulfonium salts is usually carried outabout 2070 C. At much lower temperatures, the reaction rate is generallytoo slow for practical purposes. At temperatures appreciably higher thanabout 70C., competing reactions of the benzyl halide and solvent occur,Also, many of the resulting benzyl sulfonium salts are not thermallystable at a temperature greater than about 70 C. Reaction at roomtemperature with substantially stoichiometric proportions of thereactants may require from several hours to several weeks to achieveessentially complete conversion. However, the extent of the reaction isreadily followed by analysis of the reaction mixture for ionic halide.Competing solvolysis is detected by titration for by-product acid.

Normally, the sulfonium salt prepared as described above will have achloride or bromide countertanion. But if desired, the halide sulfoniumsalt can be converted to another anionic salt by standard techniquessuch as passing a solution of the water-soluble sulfonium halide throughan anion exchange column in the desired salt form. Other commoncounteranions which may be employed include such inorganic and organicanions as fluoride, iodide, sulfate, nitrate, bicarbonate, carbonate,acetate, propionate, etc. Generally monovalent anions are mostconvenient, although the nature of the counteranion is not criticalprovided that the sulfonium salt is watersoluble.

Other methods for the synthesis of these sulfonium salts will beapparent in light of this disclosure tothose skilled in the art.

The thermal stability of the claimed sulfonium salts depends upon theirexact structure. While dilute solutions of the salts are generallystable at room temperature, isolation and purification of the salts evenby such techniques as freeze drying is often difficult. Fortunately, formany purposes the initial salt solutions can be used. But even in dilutesolution these sulfonium salts are generally thermally unstable attemperatures greater than about 70 C. For example, heating a 0.175 M(6.3 wt. percent) solution of dimethyl(p-dodecylbenzyl)sulfoniumchloride in deionized water for 8 hours at 90 C. destroyed about 90% ofthe original surfactant activity as shown by surface tensionmeasurements. The thermal stability of other salts is similar, althoughthere is sufficient variation so that appropriate fugitive cationicsurfactants can be selected for varied applications and conditions.

The exact nature of the thermal conversion of these sulfonium salts fromactive surfactants to essentially inert hydrophobic materials is notfully understood. However an alkylbenzyl alcohol and alkyl sulfide havebeen recovered and identified after heating a salt in aqueous solution.

The novel heat labile or fugitive sulfonium surfactants described.herein have many applications. Particularly important is their use assurfactants in aqueous film-forming emulsions which because thesurfactant can be destroyed when the film is dried give films withimproved water resistance. These characteristics are highly advantageousin many products and processes such as the application of waterrepellant textile finishes, textile sizing, paper coatings, and in latexpaint and wax formulations.

The invention disclosed herein will be further illustrated by thefollowing representative specific embodiments which set forth the bestmode contemplated by the inventor of carrying out his invention. Unlessotherwise specified, all parts and percentages are by weight.

Example 1. Dimethyl(p dodecylbenzyl)sulfonium chloride (I) (A) To anaqueous mixture of 6.21 g. (0.1 mole) of dimethyl sulfide was added 29.5g. (0.1 mole) of pdodccylbenzyl chloride. After diluting to 100 ml., theheterogeneous mixture was shaken at room temperature for 2 to 3 weeks toobtain a clear, homogeneous solution. The conversion as determined byanalysis for ionic chloride was essentially complete. Titration forby-product acid indicated less than 1% hydrolysis.

In subsequent preparations methanol and mixtures of methanol and waterhave been used to give a more homogeneous solution throughout thereaction period. Using equimolar amounts of 1 N solutions of dimethylsulfide and p-dodecylbenzyl chloride in methanol, the reaction to formthe sulfonium chloride (1) was 81% complete in 48 hours.

Visible evidence of the surfactant properties of the sulfonium solutionswas the appreciable foaming observed when the mixtures were shakenduring synthesis. Further evidence of surfactant activity is provided bythe surface tension data given in Table 1. These data were obtained witha DuNuoy tensiometer using standard procedures and appropriate dilutionsof an aqueous solution of the sulfonium chloride (1).

TABLE 1.SURFAOE TENSION OF AQUEOUS SOLUTIONS (B) To establish thefugitive nature of this surfactant, a 0.175 molar solution of I indeionized water was heated in a constant temperature bath at C. Sampleswere removed at various time intervals, cooled, diluted to a standardconcentration of 0.006 M and the surface tension determined. Over aperiod of 8 hours, the surface tension increased from the minimum valueof 36.7 dynes/cm. to a value of 48.5 dynes/cm. Comparison of these datawith a calibration curve prepared from Table 1 indicates that about 75%of the original surfactant was destroyed in 4 hours heating and about90% in 8 hours.

(C) The fugitive nature of this surfactant 'was also shown in a testmeasuring the amount of a 0.175 M solution of I required to coagulateand flocculate ml. portions of a 0.5 wt. percent bentonite slurry. Theunheated solution was highly effective, 0.10 ml. bringing aboutflocculation. However, after 4 hours heating at 90 C., 0.20 ml. wasrequired, and after 16 hours heating 0.50 ml. was still insufficient toflocculate the standard clay suspension.

(D) Using a styrene-butadiene latex prepared with 2- aminoethylmethacrylate hydrochloride as a built-in surfactant, a latex which hasthe property of irreversibly coagulating upon exposure to ammonia vaporsin the absence of another cationic or non-ionic surfactant, the thermaldegradation of the fugitive cationic emulsifier was furtherdemonstrated. One drop of the 0.175 M solution of I preventedcoagulation of a 4.00 ml. sample of the latex on exposure to ammonia.After 30 minutes heating at 90 C., 2 drops of the fugitive surfactantwere required, and after 16 hours heating, even 15 drops wereinsufficient to inhibit the latex coagulation.

Example 2.--Dimethyl(p-ethylbenzyl)sulfonium chloride (II) In a mannersimilar to that described in Example 1, dimethyl(p-ethylbenzy1)sulfoniumchloride was prepared by shaking an aqueous solution containing 6.21 g.(0.1 mole) of dimethyl sulfide and 15.45 g. (0.1 mole) of p-ethylbenzylchloride. The final clear aqueous solution showed little visiblesurfactant characteristics upon shaking. The surface tension of a 0.05 Msolution was 51.1 dynes/cm., and there was no appreciable change after20 hours of heating at 90 C. Clearly, this material, outside the scopeof this invention, does not display the desired fugitive cationicsurfactant properties.

Example 3.--p-Butylbenzyldimethylsulfonium chloride (A) To illustrate analternate synthesis, 25 parts (0.152 mole) of p-butylbenzyl alcohol wasstirred with 29 parts (0.152 moles) of p-toluenesulfonic acidmonohydrate and 43.7 parts (0.7 moles) of dimethylsulfide for 6 days atroom temperature. Then 250 parts of water was added to extract thewater-soluble product. After extracting the aqueous phase three timeswith benzene, the aqueous solution was concentrated in vacuo to a totalof 220 parts. This aqueous concentrate was passed through a bed ofquaternary ammonium anion-exchange resin in OH- form and thenneutralized with HCl to give an aqueous solution 0.613 N inp-butylbenzyldimethylsulfonium chloride.

(B) As an initial test of the emulsifying action ofp-butylbenzyldimethylsulfonium chloride, the following mixtures wereprepared in 25 ml. volumetric flasks:

(a) 25 ml. H O+1 ml. toluene;

(b) 12.5 ml. of 0.163 N butylbenzyldimethylsulfonium chloride-H25 ml. HO+1 ml. toluene; and

(c) 25 ml. of 0.163 N butylbenzyldimethylsulfonium chloride-l-l ml.toluene.

On shaking slight foaming was observed with solutions (b) and (c).Solubilization of toluene (c) was too small to detect and the mixturesunderwent rapid phase separation on standing. In contrast mixtures oftoluene with dilute aqueous dodecylbenzyldimethylsulfonium chloride (I)exhibited strong foaming, delayed phase TABLE 2.EMULSION POLYMERIZATIONTESTS p-ethylbenzyl chloride and n-butyl 3-methylthiopropionate. Asample of this solution was diluted to 0.175 M with deionized water andthe thermal stability at 90C. was examined by surface tensionmeasurements after a standard dilution to about 0.005 M. An increasefrom 48.0 to 54.3 dynes/cm. was found in 7 hours heating. In thebcntonite flocculation test as described in Example 1(C), 0.15 ml. ofthe 0.175 M solution of VI was required to achieve flocculation afterone hour of heating at 90C., 0.25 ml. after 8 hours, and 0.45 ml. after20.5 hours heating, thus indicating again the fugitive nature of thesecationic surfactants.

Run Sult'onium Salt Polymerization Results ArOHzSMezCl Conditions 2-1p-Dodecylbenzyl (I)... 16 hrs; 50 (1...... Good latex. 2-2 p-Butylbenzyl(III).. 128 hrs; 50 C Moderately cloudy aqueous phase. 2-3 Benzyl (IV)128 hrs; 50 C Essentially clear aqueous phase.

1 Another 3.3 parts of 30% E201 was added after 16 hrs.

Example 4.(2-carbomethoxyethyl) (p-ethylbenzyl) methylsulfonium chloride(V) (A) A mixture of 15.45 g. (0.1 mole) of p-ethylbenzyl chloride and13.4 g. (0.1 mole) of methyl 3-methylthiopropionate in 100 ml. of 95%aqueous methanol was shaken for one hour at room temperature until theturbidity cleared and then allowed to stand for several weeks to insurecomplete reaction. By chloride analysis, the reaction was at least 96%complete.

(B) A sample of the above methanolic solution was diluted to 0.175 M forthermal stability study. This solution was heated at 90C. with periodicsampling followed by dilution to about 0.005 M and measurement of thesurface tension. The minimum surface tension was 43.2 dynes/om. with anincrease after 4 hours of heating to 49.9 dynes/cm. and after 1-6 hoursto 53.1 dynes/cm., e.g., a loss of at least 80% of the initialsurfactant activity in 16 hours.

(C) The surfactant properties of the sulfonium solution is further shownin a flocculation test with coal fines. Thus vigorous hand shaking of amixture of 2.0 ml. of the initial methanolic solution of V, 18 ml. ofwater and 100 mg. of standard Peabody coal fines gives a suspensionwhich separates into large fiocs of coal fines and a clear supernatantliquor less than seconds after the agitation is stopped. In a controlexperiment using 2.0 ml. of water for the sulfonium solution asuspension was obtained which was still dispersed after minutes. Heatingthe solution of VI was prepared from equimolar amounts of Example5.(2-carbobutoxyethyl) (p-ethylbenzyl) methy-lsulfonium chloride (VI) Ina manner as described in Example 4A, a methanolic solution of VI wasprepared from equimolar amounts of I claim:

1. A water-soluble sulfonium salt of the formula:

R1 ,l.Y R1

wherein (1) R is a C -C alkyl group, and R and R are independently a C-C alkyl or C -C hydroxyalkyl group; or

(2) R is a C C alkyl group, R is a C -C alkyl group, and R is a group ofthe formula:

(CnHzn) i l 0 R4 wherein R is a C -C alkyl group, and n is an integerfrom 1 to 4; and Y is an anion. 2. The sulfonium salt of claim 1 whereinR is methyl. 3. The sulfonium salt of claim 1 wherein R is a Ca-Cu;alkyl group.

4. The sulfonium salt of claim 3 wherein R is dodecyl and R and R aremethyl.

5. Dirnethyl (p-dodecylbenzyl) sulfonium chloride. 6. The sulfonium saltof claim 1 wherein R is ethyl, R is methyl, and R is CH CH COOR 7. Thesulfonium salt of claim 1 wherein the counteranion is monovalent.

8. The sulfonium salt of claim 7 wherein the counteranion is chloride.

References Cited UNITED STATES PATENTS 2,178,353 9/1939 Werntz 260-6072,193,963 3/1940 Harris 260-607 OTHER REFERENCES Mamalis, J. Chem. Soc.(London), '1960, pp. 4747- Reid, Org. Chem. of Bivalent Sulfur, 'vol. II(1960), pp. 66-75.

LORRAINE A. WEINBERGER, Primary Examiner. M. G. BERGER, AssistantExaminer.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,409,660 November 5, 1968 William G. Lloyd It is certified that errorappears in the above identified patent and that said Letters Patent arehereby corrected as shown below:

Column 4, line 60, "0.613" should read 0.163 Column S, cancel "VI wasprepared from equimolar amounts of" and insert V destroys thisflocculent activity Signed and sealed this 10th day of March 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer

